package org.apache.lucene.util.fst;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.store.DataInput;
import org.apache.lucene.store.DataOutput;

/**
 * Output is a long, for each input term.  NOTE: the
 * resulting FST is not guaranteed to be minimal!  See
 * {@link Builder}.  You cannot store 0 output with this
 * (that's reserved to mean "no output")!
 *
 * @lucene.experimental
 */

public final class PositiveIntOutputs extends Outputs<Long> {

    private final static Long NO_OUTPUT = new Long(0);

    private final boolean doShare;

    private final static PositiveIntOutputs singletonShare = new PositiveIntOutputs(true);
    private final static PositiveIntOutputs singletonNoShare = new PositiveIntOutputs(false);

    private PositiveIntOutputs(boolean doShare) {
        this.doShare = doShare;
    }

    public static PositiveIntOutputs getSingleton(boolean doShare) {
        return doShare ? singletonShare : singletonNoShare;
    }

    public Long get(long v) {
        if (v == 0) {
            return NO_OUTPUT;
        } else {
            return Long.valueOf(v);
        }
    }

    @Override
    public Long common(Long output1, Long output2) {
        assert valid(output1);
        assert valid(output2);
        if (output1 == NO_OUTPUT || output2 == NO_OUTPUT) {
            return NO_OUTPUT;
        } else if (doShare) {
            assert output1 > 0;
            assert output2 > 0;
            return Math.min(output1, output2);
        } else if (output1.equals(output2)) {
            return output1;
        } else {
            return NO_OUTPUT;
        }
    }

    @Override
    public Long subtract(Long output, Long inc) {
        assert valid(output);
        assert valid(inc);
        assert output >= inc;

        if (inc == NO_OUTPUT) {
            return output;
        } else if (output.equals(inc)) {
            return NO_OUTPUT;
        } else {
            return output - inc;
        }
    }

    @Override
    public Long add(Long prefix, Long output) {
        assert valid(prefix);
        assert valid(output);
        if (prefix == NO_OUTPUT) {
            return output;
        } else if (output == NO_OUTPUT) {
            return prefix;
        } else {
            return prefix + output;
        }
    }

    @Override
    public void write(Long output, DataOutput out) throws IOException {
        assert valid(output);
        out.writeVLong(output);
    }

    @Override
    public Long read(DataInput in) throws IOException {
        long v = in.readVLong();
        if (v == 0) {
            return NO_OUTPUT;
        } else {
            return v;
        }
    }

    private boolean valid(Long o) {
        assert o != null;
        assert o instanceof Long;
        assert o == NO_OUTPUT || o > 0;
        return true;
    }

    @Override
    public Long getNoOutput() {
        return NO_OUTPUT;
    }

    @Override
    public String outputToString(Long output) {
        return output.toString();
    }
}
